The introduction of surfactant for treatment of infants with Respiratory Distress Syndrome has been an important clinical advance. However, the mechanisms responsible for surfactant function at the molecular level remain incompletely understood. The basic hypothesis of this proposal is that hydrophobic surfactant proteins (SP-B and SP-C) have unique conformations that enable them to insert into lipid monolayers and bilayers in a manner that allows specific protein-protein and lipid-protein interactions that are important for optimal biological activity. Our work and that of others has led to the belief that under reducing conditions SP- B has a predominantly amphipathic alpha-helical structure that lies horizontally in the plane of a lipid monolayer. In contrast, SP-C is a very hydrophobic helical protein and has an orientation perpendicular to the plane of the lipid monolayer. Verification and refinement of these models requires understanding the effects of oxidation on monomers, palmitoylation of SP-C, conformations of the proteins in lipid, and the degree and angle of insertion of the proteins in lipids. A variety of spectroscopic techniques including circular dichroism (CD), Fourier transform infrared (FTIR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR), as well as biophysical and physiological measures of surfactant function are proposed to address these questions. A unique aspect of this proposal is the use of synthetic proteins that emulate results found using native proteins. Animal studies of surfactant function include three different models of surfactant insufficiency or inactivation. These detailed studies should provide a better picture of the molecular architecture of surfactant lipids and the hydrophobic surfactant proteins and should help define synthetic lipid-peptide formulations that may further optimize surfactant therapy.